During the 1970's, chisel plows became popular in the corn belt of the United States, replacing many moldboard plows for fall primary tillage.
A chisel plow creates a series of grooves or furrows left by the chisel shanks and ridges created by soil thrown laterally by the plow points. However, with high ridges left in the fall, preparing the soil for planting in the spring became more difficult because discs or other surface preparation implements had to be operated much deeper to level the ridges, and leveling was not always achieved with conventional disc gangs because they throw soil in the same direction, at least for sections of the disc gangs which span over two or more ridges formed by the chisel plow.
In an effort to reduce the size of the ridges left by the chisel plow, the chisels were run at a deeper operating depth, e.g., 12-14 in. But this created other problems. For many years, it was believed that the ridge created between adjacent chisel shanks was desirable. The top of the ridge dries out first, which was believed to be desirable for preparing the soil early for planting. However, the resulting deep furrows left by the chisel shanks cause soil erosion problems; and large weeds growing in the bottom of the groove are difficult to kill in the wet conditions of spring and with the lighter tillage normally used in spring.
During the 1980's, various soil leveling arrangements were introduced to the marketplace. One general method was to mount a trailing toolbar behind the rear chisel shanks. Shanks with points of various configuration were attached to the trailing toolbar. The points were centered on the ridge between adjacent chisel shanks in the rear row to break up the ridge. This resulted in smaller ridges being formed closer together rather than, for example, one large ridge. Thus, for example, two smaller ridges spaced at 15" were formed rather than one large ridge with a 30" spacing. This formed a smoother soil surface and also permitted much shallower disc operation in the spring. However, the leveler shanks caused bunching of residue, or trash, and they frequently pulled bunches of residue to the surface leaving some fields with too much exposed residue. The leveler shanks would also frequently become plugged with residue, as the residue straddled the shank being pulled through the soil.
Some farmers installed single disc gangs on the rear of their chisel plows. This did not prove entirely satisfactory. One problem was ridging, since each gang moved the soil in only one direction. The random spacing of each disc blade relative to its associated shank also caused some of the blades to actually move soil toward rather than away from the ridge formed by a pair of adjacent chisel plow shanks. Other approaches made use of a large single blade placed between adjacent shanks to "knock down" the top of the ridge. This approach moved soil away from the ridge in one direction only and did not totally eliminate the soil ridging problem.